From mboxrd@z Thu Jan  1 00:00:00 1970
From: arnd@arndb.de (Arnd Bergmann)
Date: Wed, 21 May 2014 16:56:46 +0200
Subject: [PATCH V5 18/20] ARM: exynos: cpuidle: Pass the AFTR callback to
 the platform_data
In-Reply-To: <537C6BA5.5080909@linaro.org>
References: <1397212815-16068-1-git-send-email-daniel.lezcano@linaro.org>
 <11675203.TylGKV1VBZ@wuerfel> <537C6BA5.5080909@linaro.org>
Message-ID: <5367019.Bht3ZqI0ij@wuerfel>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wednesday 21 May 2014 11:02:29 Daniel Lezcano wrote:
> On 05/21/2014 10:10 AM, Arnd Bergmann wrote:
> > On Wednesday 21 May 2014 09:15:34 Daniel Lezcano wrote:
> >> On 05/15/2014 10:40 PM, Kukjin Kim wrote:
> >>
> >> [ ... ]
> >>
> >>>>>> Exynos cpuidle is not a device on the SoC, so I don't think there is
> >>>>>> any
> >>>>>> way to represent it in DT. The only thing I could see this is matching
> >>>>>> root node with a central SoC driver that instantiates specific
> >>>>>> subdevices, such as cpufreq and cpuidle, but I don't see any available
> >>>>>> infrastructure for this.
> >>>>>
> >>>>> There is a RFC for defining generic idle states [1].
> >>>>>
> >>>>> The idea behind using the platform driver framework is to unify the code
> >>>>> across the different drivers and separate the PM / cpuidle code.
> >>>>>
> >>>>> By this way, we can move the different drivers to drivers/cpuidle and
> >>>>> store them in a single place. That make easier the tracking, the review
> >>>>> and the maintenance.
> >
> > Yes, that would be great. I only looked briefly at the series now, doesn't
> > that require the use of psci?
> 
> No, because PSCI is for some specific platform (eg. calxeda), all the 
> other drivers are legacy and manually handling the PM via some low level 
> callbacks. This is why all drivers were implemented all over the place 
> making so difficult to maintain them. Little by little, we split the PM 
> callbacks from the idle algorithm so reducing the platform dependency 
> with the generic code.
>
> The PSCI implements such PM callbacks in the firmware directly and are 
> accessed through an API. PSCI is, let's say some kindof nextgen cpuidle. 
> It is similar than mwait on Intel. But if a new platform does not have 
> such firmware, then the cpuidle driver will have the legacy format.

Ok, thanks for the exlanation.

	Arnd